The invention relates to a ventilation device for a fuel tank of a motor vehicle, having lines guided out of the fuel tank including at least a line for operational ventilation and a line for refuelling ventilation.
Ventilation devices are frequently used in fuel tanks of motor vehicles. They include lines which are each guided to a compensator reservoir provided near the filler neck of the fuel tank. These compensator reservoirs each have a connection to the environment via a common activated carbon filter. Pressure compensation of the fuel tank therefore takes place via the compensator reservoirs and via the lines during refuelling of the motor vehicle and during operation of the internal combustion engine of the motor vehicle.
A disadvantage of the known ventilation devices is that the fuel tank, including the ventilation device, has a very large surface area. A particularly large amount of fuel can pass into the environment via this very large surface area by, for example, diffusion through the walls of the lines. Furthermore, there are a plurality of connecting lines, such as, for example, refuelling ventilation and operational ventilation lines (hereinafter, collectively the xe2x80x9clinesxe2x80x9d), and therefore a plurality of connecting points through which fuel vapor can diffuse. This makes it impossible to obey emission legislation in many locations and/or countries.
The invention is based on the problem of designing a ventilation device so that a particularly small amount of fuel vapor escapes into the environment.
This problem is solved according to the invention by the compensator reservoirs being integrated in the tank, and by the lines having a mutually adjacent wall, at least in a subregion situated outside the fuel tank (the xe2x80x9csubregionxe2x80x9d).
The result of this design is that in the subregion the two lines share an outer wall, and therefore an entire surface area. This reduces the total surface area of the lines and the number of connecting points. This reduction in the surface area of the lines and in the number of connecting points achieves a reduction in the permeation of fuel vapors.
According to an advantageous embodiment of the invention, the escape of fuel vapors can be further reduced if the shared outer wall of the two lines is essentially of cylindrical design. By this means, the two lines have a particularly small, shared surface area.
According to an advantageous embodiment of the invention, the escape of fuel vapors can be further reduced if the lines in the subregion are arranged with one surrounding the other.
According to another advantageous embodiment of the invention, when lines are arranged one surrounding the other, securing the inner line proves to be particularly simple if the inner line is connected to the outer line via at least one web.
According to another advantageous embodiment of the invention, the manufacturing of the lines proves to be particularly cost effective if the inner line is fastened directly to the outer line.
During refuelling, a large volume of air mixed with fuel vapors is generally conveyed out of the fuel tank. According to another advantageous embodiment of the invention, this air is better able to escape if the line for the refuelling ventilation has a larger diameter than the line for the operational ventilation.
According to another advantageous embodiment of the invention, the ventilation device requires a particularly small constructional outlay if the line for the operational ventilation opens into the line for the refuelling ventilation instead of guiding both lines to the activated carbon filter, as is done in prior art devices.
According to another advantageous embodiment of the invention, penetration of fuel from the operational ventilation line into the refuelling ventilation line can be avoided in a simple manner if the opening of the line for the operational ventilation into the line for the refuelling ventilation is arranged at a height which avoids an overflowing of fuel when the motor vehicle is in a sloping position. This arrangement of the lines also has the advantage that the fuel, which travels through the line for the operational ventilation, can return through the line for the refuelling ventilation.
According to another advantageous embodiment of the invention, an incorrect flow of fuel vapors through the lines can be avoided in a simple manner if the line for the operational ventilation can be closed by a valve. A further advantage of this design is that when the line for the operational ventilation is closed by the valve, displacement of the air in the line for the operational ventilation is avoided during the fuel tanking procedure, thus avoiding overfilling the fuel tank during this tanking procedure. The valve can be switched between the open and closed positions electromagnetically or mechanically or can be actuated by the high speed of flow in the operational ventilation or refuelling ventilation lines.
According to an advantageous embodiment of the invention, the escape of fuel vapors can be further reduced if a compensator reservoir, which is arranged in one of the lines, shares a wall with the other line or with another compensator reservoir arranged in the other line.
According to another advantageous embodiment of the invention, direct escape of the fuel vapors from the compensator reservoirs into the environment can be reliably prevented if the compensator reservoirs are arranged within the fuel tank. The connecting points of the lines to the compensator reservoirs can therefore, likewise be arranged within the fuel tank. This leads to a further reduction in the escape of fuel vapors.
The ventilation device according to the invention proves to have a particularly simple structure if the compensator reservoirs, which are arranged within the fuel tank, are arranged such that one is below the other, and if the line for the operational ventilation is guided through the compensator reservoir for the line for the refuelling ventilation. By this means, the lines can be designed with one surrounding the other as soon as they leave the compensator reservoirs. The compensator reservoirs and the lines are therefore designed as a unit which is particularly simple to handle. The lines may, for example, be screwed to the compensator reservoirs or fastened to the compensator reservoirs by welding.
The invention permits numerous embodiments. In order to further clarify its basic principle, two of these are illustrated in the drawing and are described below.